Macrophagic myofasciitis

A rare acquired skeletal muscle disease characterized by infiltration of the epimysium, perimysium, and perifascicular endomysium by macrophages with crystal inclusions composed of aluminum salts at the site of a previous vaccination (most commonly the deltoid muscle). Muscle necrosis is typically absent. Patients may present with myalgias, arthralgias, muscle weakness, chronic fatigue, asthenia, fever, and cognitive dysfunction. Signs and symptoms usually develop slowly over several months.